U.S. patent number 10,118,163 [Application Number 15/662,756] was granted by the patent office on 2018-11-06 for methods for producing hierarchical mesoporous zeolite beta.
This patent grant is currently assigned to Saudi Arabian Oil Company. The grantee listed for this patent is Saudi Arabian Oil Company. Invention is credited to Ke Zhang.
United States Patent |
10,118,163 |
Zhang |
November 6, 2018 |
Methods for producing hierarchical mesoporous zeolite beta
Abstract
Embodiments of the present disclosure are directed to a method
of producing hierarchical mesoporous zeolite beta. The method
comprises providing a parent zeolite beta with a silicon to
aluminum molar ratio of 5 to 50. The method further comprises,
mixing the parent zeolite beta with an aqueous metal hydroxide
solution and heating the parent zeolite beta and aqueous metal
hydroxide mixture to a temperatures greater than or equal to
100.degree. C. to produce the hierarchical mesoporous beta zeolites
having and average pore size greater than 8 nm. In embodiments, the
hierarchical mesoporous beta zeolites are produced without a
templating agent or pore-directing agent.
Inventors: |
Zhang; Ke (Stoneham, MA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Saudi Arabian Oil Company |
Dhahran |
N/A |
SA |
|
|
Assignee: |
Saudi Arabian Oil Company
(Dhahran, SA)
|
Family
ID: |
60191483 |
Appl.
No.: |
15/662,756 |
Filed: |
July 28, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J
35/109 (20130101); C01B 39/46 (20130101); B01J
29/7007 (20130101); B01J 37/10 (20130101); B01J
35/1061 (20130101); B01J 37/04 (20130101); C01B
39/026 (20130101); B01J 35/1038 (20130101); C01P
2006/14 (20130101); C01P 2006/16 (20130101); C01P
2002/72 (20130101) |
Current International
Class: |
C01B
39/02 (20060101); B01J 29/70 (20060101); C01B
39/46 (20060101); B01J 37/10 (20060101); B01J
37/04 (20060101); B01J 35/10 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Groen et al (2008), Mesoporous beta zeolite obtained by
desilication, Microporous and Mesoporous Materails 114 (2008)
93-102. cited by examiner .
Liu, J. et al.; Alkaline-Acid Treated Mordenite and Beta Zeolites
Featuring Mesoporous Dimensional Uniformity; Materials Letters;
Jun. 14, 2014; pp. 78-81; vol. 132; Elsevier. cited by applicant
.
Perez-Ramirez, J. et al.; Tailored Mesoporosity Development in
Zeolite Crystals by Partial Detemplation and Desilication; Advanced
Functional Materials; Jan. 9, 2009; pp. 1640172; vol. 19, No. 1;
Wiley-VCH GmbH & Co. cited by applicant .
dos Santos, L.R.M. et al; Creation of Mesopores and Structural
Re-Organization in Beta Zeolite During Alkaline Treatment;
Microporous and Mesoporous Materials; Feb. 4, 2016; pp. 260-266;
vol. 226; Elsevier. cited by applicant .
Groen, J.C. et al.; On the Introduction of Intracrystalline
Mesoporosity in Zeolites Upon Desilication in Alkaline Medium;
Microporous and Mesoporous Materials; Apr. 8, 2004; pp. 29-34; vol.
69, No. 1-2; Elsevier Inc. cited by applicant .
International Search Report and Written Opinion pertaining to
Application No. PCT/US2017/056085 dated Feb. 16, 2018. cited by
applicant .
Ding et al.,"LCO hydrotreating with Mo--Ni and W--Ni supported on
nano- and micro-sized zeolite beta", Applied Catalysis A: General
353, pp. 17-23 (2009). cited by applicant .
Li et al., "Realizing the Commercial Potential of Hierarchical
Zeolites: New Opportunities in Catalytic Cracking", ChemCatChem,
vol. 6, pp. 46-66 (2014). cited by applicant .
Mitchell et al., "Structural analysis of hierarchically organized
zeolites", Nature Communications, DOI: 10.1038/ncomms9633, pp.
1-14, Oct. 20, 2015. cited by applicant .
Verboekend et al., "Mesopore Formation in USY and Beta Zeolites by
Base Leaching: Selection Criteria and Optimization of
Pore-Directing Agents", Crystal Growth & Design, vol. 12, pp.
3123-3132 (2012). cited by applicant .
Verboekend et al., "Hierarchical Y and USY Zeolites Designed by
Post-Synthetic Strategies", Adv. Funct. Mater., vol. 22, pp.
916-928 (2012). cited by applicant .
Zhang et al., "Optimization of Hierarchical Structures for Beta
Zeolites by Post-Synthetic Base Leaching", Ind. Eng. Chem. Res,
vol. 55, pp. 8567-8575 (2016). cited by applicant .
Moeller et al., "Mesoporosity--a new dimension for zeolites", Chem.
Soc. Rev., vol. 42, pp. 3689-3707 (2013). cited by
applicant.
|
Primary Examiner: Brunsman; David M
Attorney, Agent or Firm: Dinsmore & Shohl LLP
Claims
What is claimed is:
1. A method for producing hierarchical mesoporous beta zeolites
comprising: providing parent beta zeolites having a molar ratio of
silicon to aluminum of from 5 to 50; mixing the parent beta
zeolites with an aqueous metal hydroxide solution, where the
aqueous metal hydroxide is an alkali metal hydroxide or an alkali
earth metal hydroxide, or both; and heating the parent beta
zeolites and aqueous metal hydroxide mixture at an autogenous
pressure to a temperature greater than or equal to 100.degree. C.
to produce the hierarchical mesoporous beta zeolites having an
average pore size greater than 8 nanometers; where the hierarchical
mesoporous beta zeolites are produced without a templating agent or
a pore-directing agent; and where the produced hierarchical
mesoporous beta zeolites have a total pore volume greater than or
equal to 0.30 cm.sup.3/g.
2. A method of claim 1, where the parent beta zeolites have a molar
ratio of silicon to aluminum of from 10 to 25.
3. A method of claim 1, where the parent beta zeolite and aqueous
metal hydroxide mixture is heated to a temperature greater than
100.degree. C.
4. A method of claim 1, where the parent beta zeolite and aqueous
metal hydroxide mixture is heated for a time interval of greater
than or equal to 1 hour.
5. A method of claim 1, where the produced hierarchical mesoporous
beta zeolites exhibit an x-ray diffraction peak at 2.THETA. from 7
degrees to 9 degrees and another x-ray diffraction peak at 2.THETA.
from 21 degrees to 23 degrees.
6. A method of claim 1, where the produced hierarchical mesoporous
beta zeolites have a peak pore size of greater than or equal to 20
nanometers.
7. A method of claim 1, where the pH of the parent beta zeolites
and aqueous metal hydroxide mixture is greater than or equal to
12.
8. A method of claim 1, where the concentration of the aqueous
metal hydroxide solution has a concentration from 0.01 M to 10 M.
Description
BACKGROUND
Technical Field
This disclosure relates to methods for producing mesoporous zeolite
beta. More specifically, this disclosure relates to method for
producing hierarchical mesoporous zeolite beta without a templating
agent or a pore-directing agent.
Background
Zeolite beta is a crystalline aluminosilicate used as a catalyst,
molecular sieve, filter, adsorbent, drying agent, cation exchanger,
dispersing agent, and detergent builder. Zeolite beta can be used
as a catalyst in, for example, alkylation reactions, acylation
reactions, tetrahydropyranyl ether synthesis reactions, ketone
reduction reactions. The petrochemical and chemical industries use
zeolite beta in alkylation and acylation reactions, catalytic
cracking, and isomerization. Zeolite beta is used because it has a
large surface area per unity mass, a large ion-exchange capacity,
strong acidity, and stability at high temperatures.
Different zeolites such as zeolite A, zeolite beta, mordenite, and
zeolite Y vary in pore structure, pore size, acidity, acid site
strength, acid site distribution, and stability. These intrinsic
differences make the applications of one zeolite different than the
applications of another. Zeolite beta is often chosen for its
stability at elevated temperatures and the compatibility of its
acid sites with hydrocracking reactions. Hydrocracking reactions
break up hydrocarbon feed or hydrocarbon fraction into smaller
molecules. Typical hydrocarbon feedstocks for hydrocracking
reactions using zeolite beta include vacuum gas oil, deasphalted
gas oil, and light cycled oil.
Zeolite beta has micropores--that is, pores with diameters less
than or equal to 2 nanometers (nm). Specifically, pores of zeolite
beta have a pore size of from 0.5 nm to 1 nm. As a result, zeolite
beta is not effective with reactants larger than the 2 nm diameter
of the mesopores of zeolite beta. Further, using zeolite beta with
reactants larger than 2 nm can cause coking of the reactants onto
the zeolite beta, reducing catalytic efficiency and shortening the
catalytic life of the zeolites. To solve these deficiencies of
using zeolite beta as a catalyst, zeolite beta with hierarchical
mesopores may also be used. Hierarchical mesoporous zeolite beta
has micropores and mesopores, pores with a diameter greater than 2
nm and less than 50 nm. The mesopores facilitate the transport of
molecules to the catalytic sites and reduce the diffusion
limitations of these molecules.
Hierarchical mesoporous zeolites may be produced by conventional
techniques known in the art, but these techniques have advantages
and disadvantages. One technique, known as "top-down" synthesis,
involves the chemical erosion of microporous zeolite beta to create
mesopores. In "top-down" synthesis, the chemical agent used to
dissolve the aluminosilicate framework to create mesopores also
decreases the crystallinity of the zeolite. Traditionally,
"top-down" synthesis is performed at temperatures around 65.degree.
C.; higher temperatures, closer to 100.degree. C., are believed to
further decrease the crystallinity of the zeolite. The decreased
crystallinity of the zeolite results in less catalytically active
sites and overall decreased catalytic efficiency for the zeolite
beta. Pore-directing agents may be used in top-down synthesis to
protect zeolite crystallinity during the chemical treatment of the
zeolites. Mesopores created by "top-down" synthesis are also formed
in a random and unpredictable pattern on the surface of zeolite
beta and have an average pore size from 2 nm to 5 nm.
Another technique, known as "bottom-up" synthesis starts with
zeolite precursors--sometimes a gel or solution--and builds
hierarchical mesoporous zeolites around a templating agent. While
"bottom-up" synthesis allows for more control of where the
mesopores form and preserves the crystallinity of the zeolite beta,
the templating agents are costly and conventionally must be used in
large quantities. Further, the use of templating agents or
pore-directing agents also requires additional time and labor
intensive steps to separate the agents from the zeolite beta.
SUMMARY
Therefore, there exists a need for a method for producing
hierarchical mesoporous zeolite beta that preserves the
crystallinity of the zeolite beta without using a templating agent
or a pore-directing agent. Embodiments relate to synthesizing
hierarchical mesoporous zeolite beta in reaction conditions similar
to traditional "bottom-up" synthesis, but using existed microporous
beta zeolites as in conventional "top-down" synthesis. The
resulting zeolites are mesoporous while surprisingly retaining
crystallinity and acidity.
The produced hierarchical mesoporous zeolite beta may be used as a
catalyst in a hydrocracking reaction. In one or more embodiments,
the hierarchical mesoporous zeolite beta has mesopores to allow for
the catalytic reaction of molecules too large to enter zeolite beta
micropores, that is, molecules larger than 2 nm. Additionally,
embodiments allow for a reduction in diffusion limitation for from
0.5 nm to 1 nm molecules. In embodiments, the produced hierarchical
mesoporous zeolite beta also retains the crystallinity and acidity
of the parent zeolite beta.
Embodiments of the present disclosure are directed to a method of
producing hierarchical mesoporous zeolite beta. The method
comprises providing a parent zeolite beta with a silicon to
aluminum ratio of at least 5. The method further comprises, mixing
the parent zeolite beta with an aqueous metal hydroxide solution
and heating the parent zeolite beta and aqueous metal hydroxide
mixture to a temperature greater than or equal to 100.degree. C. to
produce the hierarchical mesoporous beta zeolites having and
average pore size greater than 8 nm. In embodiments, the
hierarchical mesoporous beta zeolites are produced without a
templating agent or pore-directing agent.
Additional features and advantages of the described embodiments
will be set forth in the detailed description which follows, and in
part will be readily apparent to those skilled in the art from that
description or recognized by practicing the described embodiments,
including the detailed description which follows, the claims, as
well as the appended figures.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an x-ray diffraction (XRD) pattern of parent
zeolite beta as compared to two hierarchical mesoporous zeolite
beta catalysts.
FIG. 2 is a graphical depiction of the argon sorption isotherm of
parent zeolite beta as compared to two hierarchical mesoporous
zeolite beta catalysts at 87K.
FIG. 3 is a graphical depiction of the Barrett-Joyner-Halenda pore
size distribution analysis of parent zeolite beta as compared to
two hierarchical mesoporous zeolite beta catalysts.
FIG. 4 is a graphical depiction of an ammonia temperature
programmed desorption (NH.sub.3-TPD) plot of parent zeolite beta as
compared to two hierarchical mesoporous zeolite beta catalysts.
The embodiments set forth in the drawings are illustrative in
nature and not intended to be limiting to the claims. Moreover,
individual features of the drawings will be more fully apparent and
understood in view of the detailed description.
DETAILED DESCRIPTION
Embodiments of the present disclosure are directed to a method of
producing hierarchical mesoporous zeolite beta. The method
comprises providing a parent zeolite beta with a silicon to
aluminum ratio of at least 5. The method further comprises, mixing
the parent zeolite beta with an aqueous metal hydroxide solution
and heating the parent zeolite beta and aqueous metal hydroxide
mixture to temperatures greater than or equal to 100.degree. C. to
produce the hierarchical mesoporous beta zeolites having and
average pore size greater than 8 nm. In embodiments, the
hierarchical mesoporous beta zeolites are produced without a
templating agent or pore-directing agent.
As used in the present disclosure, microporous zeolites refer to
zeolite particles which have a size, as measured by their longest
dimension, of less than or equal to 100 nm. In some embodiments,
the microporous parent zeolite beta particles are present as a
single crystal structure. The parent zeolite betas may have an
average size from 1 nm to 800 nm. In other embodiments, the parent
zeolite betas may have an average size from 1 nm to 650 nm; from 1
nm to 500 nm; from 50 nm to 800 nm; from 100 nm to 800 nm; from 200
mm to 800 nm; from 200 nm to 500 nm; from 300 nm to 800 nm, or from
50 nm to 600 nm. The average size of a zeolite refers to the
averaged value of the size of all particles of a zeolite in a given
catalyst. In one or more embodiments, the provided parent zeolite
beta has a molar ratio of silicon to aluminum ratio of at least 5.
In other embodiments, the parent zeolite beta may have a molar
ratio of from 5 to 50; from 10 to 50; from 10 to 40; from 12 to 40;
from 10 to 30; or from 12 to 30.
In one embodiment, the method may include a step of providing
parent beta zeolites. The step of providing parent beta zeolites
may include process such as, by way of non-limiting example,
synthesizing the microporous parent beta zeolites or directly
acquiring the parent beta zeolites from another source. It should
be understood that multiple methods known in the art may be
available to synthesize parent beta zeolites. In one embodiment,
the step of providing parent beta zeolites includes providing a
colloidal mixture comprising parent beta zeolites, silica, alumina,
and water.
In one or more embodiments, a method for producing hierarchical
mesoporous beta zeolites may further comprise mixing the parent
beta zeolites with an aqueous metal hydroxide solution. The aqueous
metal hydroxide solution may include a single metal hydroxide
species, or may be a combination of two or more metal hydroxide
chemical species. In one embodiment, the aqueous metal hydroxide
solution comprises at least one alkali metal hydroxide, at least
one alkali earth metal hydroxide, or combinations thereof. In other
embodiments, the aqueous metal hydroxide solution may comprise
LiOH, NaOH, KOH, RbOH, Mg(OH).sub.2, Ca(OH).sub.2, Sr(OH).sub.2,
Ba(OH).sub.2, or combinations thereof. Without being limited by
theory, it is believed the mixing step evenly disperses the parent
beta zeolites and aqueous metal hydroxide solution. Mixing may
comprise stirring, swirling, vortexing, shaking, sonicating,
homogenizing, blending, similar processes, or combinations
thereof.
In one or more embodiments, the aqueous metal hydroxide solution
has a metal hydroxide concentration from 0.01 moles per liter (M)
to 10 M. In other embodiments, the aqueous metal hydroxide solution
has a concentration from 0.01 M to 5 M; 0.01 M to 3 M; 0.01 M to 1
M; 0.05 M to 1 M; 0.05 M to 0.8 M; 0.05 M to 0.5 M; or 0.1 M to 0.4
M. In one or more embodiments, the parent beta zeolite and aqueous
metal hydroxide mixture has a pH greater than or equal to 12. In
other embodiments, the parent beta zeolite and aqueous metal
hydroxide mixture has a pH greater than or equal to 13; from 12 to
14; or from 13 to 14.
In one or more embodiments, a method for producing hierarchical
mesoporous beta zeolites may further comprise heating the parent
beta zeolite and aqueous metal hydroxide mixture. In embodiments,
the heating may occur at temperatures greater than or equal to
100.degree. C. In other embodiments, the heating step may occur at
temperatures from 100.degree. C. to 500.degree. C.; from
125.degree. C. to 500.degree. C.; from 150.degree. C. to
500.degree. C.; from 175.degree. C. to 500.degree. C.; from
200.degree. C. to 500.degree. C.; from 250.degree. C. to
500.degree. C.; from 100.degree. C. to 400.degree. C.; from
100.degree. C. to 300.degree. C.; from 100.degree. C. to
250.degree. C.; from 125.degree. C. to 300.degree. C.; from
150.degree. C. to 300.degree. C.; or from 125.degree. C. to
250.degree. C. In one or more embodiments, the parent beta zeolite
and aqueous metal hydroxide mixture is heated for a time interval
of greater than or equal to 1 hour. In other embodiments, the
parent beta zeolite and aqueous metal hydroxide mixture is heated
for a time interval of from 1 hour to 16 hours; from 4 hours to 16
hours; from 16 hours to 48 hours; from 16 hours to 30 hours; from
16 hours to 24 hours; from 18 hours to 48 hours; from 18 hours to
30 hours; from 18 hours to 24 hours; or from 24 hours to 48
hours.
In one or more embodiments, a method for producing hierarchical
mesoporous beta zeolites produces hierarchical mesoporous beta
zeolites with an average pore size greater than 8 nm. Pore size can
be measured by Barrett-Joyner-Halenda (BJH) analysis. BJH analysis
measures the amount of gas that detaches from a material at 87 K
over a series of pressures. Using the Kelvin equation, of the
amount of argon adsorbate removed from the pores of the material
together with the relative pressure of the system, can calculate
the average pore size of the sample. In embodiments, the method
produces hierarchical mesoporous beta zeolites with an average pore
size from 8 nm to 25 nm; from 8 nm to 20 nm; from 10 nm to 25 nm;
from 10 nm to 20 nm; from 12 nm to 25 nm; from 12 nm to 20 nm; from
8 nm to 18 nm; from 8 nm to 16 nm; or from 12 nm to 18 nm.
Non-Local Density Functional Theory (NLDFT) method can measure the
total pore volume of the mesoporous material with the desorption
data. The NLDFT method was designed to take into account the rough
surface area of crystalline silica materials. In embodiments, the
method produces hierarchical mesoporous beta zeolites with a total
pore volume greater than or equal to 0.35 cubic centimeters per
gram (cm.sup.3/g); greater than or equal to 0.4 cm.sup.3/g; greater
than or equal to 0.45 cm.sup.3/g; or even greater than or equal to
0.5 cm.sup.3/g.
In conventional hierarchical mesoporous beta zeolite production
methods, if maintaining the crystallinity of microporous beta
zeolites is desired, then templating agents or pore-directing
agents are required. Templating agents may be calcined with the
zeolite precursor at temperatures greater than or equal to
300.degree. C. for a time intervals of at least 1 hour. After
calcination, the templating agents may be burned off the zeolite.
Templating agents of conventional hierarchical mesoporous beta
zeolite production methods may be organic or in organic in nature.
Templating agents may include, by way of non-limiting example,
hydrocarbon polymers, nitrogen doped hydrocarbon polymers,
tetraethylammonium hydroxide, imethoxsilylpropyldimethyloctadecyl
ammonium chloride, tetrapropyl ammonium hydroxide,
cetyltrimethylammonium bromide, or combinations thereof. In
embodiments, the hierarchical mesoporous beta zeolites are produced
without templating agents.
In conventional "top-down" hierarchical mesoporous beta zeolite
production methods, pore-directing agents may be incorporated into
the precursor zeolite solution and calcined at temperatures greater
than or equal to 300.degree. C. for a time interval of at least 1
hour. Pore-directing agents of conventional top-down hierarchical
mesoporous beta zeolite production methods may include cationic
surfactants and non-ionic surfactants. Cationic surfactant
pore-directing agents may include, by way of non-limiting example,
dodecyltrimethylammonium, cetyltrimethylammonium, prop
yltrimethylammonium, tetraethylammonium, tetrapropylammonium,
octyltrimethylammonium, or combinations thereof. Non-ionic
surfactant pore-directing agents may include, by way of
non-limiting example, monoamines, polyamines, or combinations
thereof. In embodiments, the hierarchical mesoporous beta zeolites
are produced without pore-directing agents. In one or more
embodiments, mesopores are created by mixing parent zeolite beta
with an aqueous metal hydroxide and heating the mixture in a teflon
lined autoclave. The mixture is heated to temperatures greater than
those conventionally used in "top-down" synthesis at an autogenous
pressure. In the alkaline solution, under the elevated pressure and
temperature, mesopores form within the beta zeolites.
Without being limited by theory, it is believed that upon
contacting the zeolite during the heating process, the alkaline
solution creates the mesopores by preferentially extracting silicon
from the zeolite framework (also known as desilication). Further,
when the temperature is above 100.degree. C. and the pressure is
above ambient atmospheric pressure, the synthetic conditions become
similar as the conventional bottom-up approach that favors
crystallization of zeolites. During this process, the appropriate
amounts of aluminum are critical in achieving hierarchical mesopore
formation while preserving zeolite crystallinity. The existence of
aluminum in the zeolite framework prevents excessive silicon
extraction by the alkaline solution and maintains a zeolite
framework with locally-desilicated area that can be recrystallized
at the synthetic conditions. Therefore, the crystallinity of the
resulting mesoporous zeolites can be preserved during the formation
of mesopores.
Crystallinity is a relative property that is generally more
relevant in "top-down" zeolite synthesis methods, since this
approach starts with parent microporous zeolites as reference
samples for direct comparison. It measures how well the acidic
sites, that is, the catalytic sites are being preserved in the
process of creating mesopores. So, for example, in a conventional
"top-down" zeolite synthesis, the crystallinity of the chemically
eroded mesoporous zeolite is compared with that of the starting
microporous zeolite. The crystallinity of two materials may be
compared by XRD. If a parent zeolite exhibits certain XRD peaks, a
mesoporous zeolite produced from the parent zeolite with preserved
crystallinity exhibits the same peaks with comparable peak
intensities. Additionally, crystallinity may be measured by
NH3-TPD. In NH3-TPD, the desorption of ammonia from a material is
measured over a range of temperatures. If a produced mesoporous
zeolite has a similar temperature of maximum desorption as the
parent zeolite, then the acidity and crystallinity were deemed as
preserved.
EXAMPLES
In the following Examples, hierarchical mesoporous beta zeolites
were compared with a microporous parent beta zeolite. The produced
hierarchical mesoporous beta zeolites maintained their
crystallinity during production, Additionally, mesopores were
formed during the production of the hierarchical mesoporous beta
zeolites.
Comparative Example A
As previously mentioned, crystallinity is a comparative property.
The crystallinity of the example hierarchical mesoporous beta
zeolites will be compared to that of their parent beta zeolites.
Comparative Example A is a microporous parent beta zeolite catalyst
with a silicon to aluminum ratio of 14.
Example 1
Example 1 is a hierarchical mesoporous beta zeolite produced from
the parent beta zeolites of Comparative Example A. First, 0.37 g of
the parent beta zeolite was mixed with 10 milliliters (mL) of 0.2M
NaOH. The resulting mixture was sealed in a Teflon lined autoclave
and placed in a heating oven at 150.degree. C. for 21 hours. The
mixture was then quenched to room temperature.
Example 2
Example 2 is a hierarchical mesoporous beta zeolite produced from
the parent beta zeolites of Comparative Example A. First, 0.37 g of
the parent beta zeolite was mixed with 10 milliliters (mL) of 0.3M
NaOH. The resulting mixture was sealed in a Teflon lined autoclave
and placed in a heating oven at 150.degree. C. for 21 hours. The
mixture was then quenched to room temperature.
FIG. 1 shows the XRD pattern for Comparative Example A, Example 1,
and Example 2. As can be seen in FIG. 1, Comparative Example A
exhibited peaks at 2-theta values of about 8 degrees and about 22.5
degrees. Examples 1 and 2 also exhibited comparable peaks at these
2-theta values. This shows that the crystallinity of the parent
beta zeolite beta was preserved in the production of the
hierarchical mesoporous beta zeolite.
FIG. 2 shows the argon sorption isotherms for Comparative Example
A, Example 1, and Example 2. The initial uptakes are related to
micropore filing, so similar initial uptakes indicate retained
crystallinity and micropore volume. As can be seen in FIG. 2, the
samples display similar initial uptakes at relative pressures less
than 0.1. This is indicative of preserved crystallinity and
microporosity in the produced hierarchical mesoporous beta zeolite.
At higher relative pressures, Examples 1 and 2 exhibit greater
argon uptake than the parent zeolite, Comparative Example A, as
well as the formation of the desorption hysteresis loop. This shows
that mesopores were created in the produced zeolites.
FIG. 3 shows the BJH analysis for Comparative Example A, Example 1,
and Example 2. The average pore width and total pore volume data
obtained from this plot is summarized in Table 1.
TABLE-US-00001 TABLE 1 NaOH Heating Average Total Pore Sample
concentration Time Pore Size Volume Comparative N/A N/A 3.8 nm 0.33
cm.sup.3/g Ex. A Example 1 0.2M 21 hours 11.1 nm 0.48 cm.sup.3/g
Example 2 0.3M 21 hours 14.4 nm 0.49 cm.sup.3/g
Table 1 shows that the total pore volume of the produced
hierarchical mesoporous beta zeolites increased by more than 45%
over the parent zeolite (Comparative Ex. A). The increase in total
pore volume is due to the creation of mesopores. FIG. 3 also shows
that peak mesopore size increased to around 25 nm for Example 1 and
to 40-50 nm for Example 2. This is represented in Table 1 by the
average pore size, which increased to 11.1 nm for Example 1 and
14.4 nm for Example 2. The increases in peak mesopore size and
average pore size are indicative of mesopore formation on the
produced hierarchical mesoporous beta zeolites.
FIG. 4 shows the NH.sub.3-TPD profiles for Comparative Example A,
Example 1, and Example 2. As can be seen in FIG. 4, Comparative
Example A exhibits one maximum desorption peak, at around
315.degree. C. Example 1 and Example 2 also exhibit one maximum
desorption peak. Example 1 has a maximum desorption at 315.degree.
C. and Example 2 has a maximum desorption at 305.degree. C. The
fact that Examples 1 and 2 shared the same maximum desorption
patterns as Comparative Example A and at about the same temperature
illustrates preserved crystallinity in the produced hierarchical
mesoporous beta zeolites.
The catalytic activity of Comparative Example A, Example 1, and
Example 2 were also compared. In mesitylene alkylation, benzyl
alcohol is consumed simultaneously via alkylation and
etherification. One reaction, the alkylation reaction, produces
1,3,5-trimethyl-2-benzylbenzene. The other reaction, an
etherification, produces dibenzyl ether. The alkylation occurs
exclusively on the external acid sites of the zeolite, because the
bulky mesitylene cannot enter the micropores of beta zeolites. The
etherification reaction occurs on both external and internal acid
sites of the zeolite. Therefore, zeolites with hierarchical
mesopores will show a decrease in selectivity, where selectivity is
calculated as twice the concentration of the ether product divided
by the concentration of the alkylation product.
While hierarchical mesoporous zeolites will show decreased
selectivity compared to their parent beta zeolites, zeolites that
have lost their crystallinity exhibit a lower benzyl alcohol
conversion as their catalytic sites have been destroyed. A
hierarchical mesoporous zeolite beta with retained crystallinity
should show decreased selectivity while maintaining the benzyl
alcohol conversion percentage. The benzyl alcohol conversion
percentage and selectivity of Comparative Example A, Example 1, and
Example 2 is shown in Table 2, for a mesitylene and benzyl alcohol
alkylation reaction at 120.degree. C. for two hours, where the
molar ratio of mesitylene to benzyl alcohol is 34.
TABLE-US-00002 TABLE 2 Benzyl Alcohol Sample Conversion Selectivity
Comparative 49.6% 2.5 Example A Example 1 84.5% 1.0 Example 2 61.6%
1.1
As can be seen from Table 2, the creation of mesopores did not
sacrifice catalytic activity by ruining crystallinity. Both Example
1 and 2 had a higher benzyl alcohol conversion rate than
Comparative Example A. Further, the decreased selectivity for
Example 1 and 2 shows that hierarchical mesopores were formed on
the zeolite.
The examples show that hierarchical mesoporous beta zeolites are
formed from treating beta zeolite with an aqueous metal hydroxide
at 150.degree. C. The mesoporous beta zeolites have a larger
average pore size and total pore volume than the parent beta
zeolites. Further, the mesoporous beta zeolites did not lose their
crystallinity or catalytic activity in the process used to create
the mesopores.
The subject matter of the present disclosure in detail and by
reference to specific embodiments thereof, it is noted that the
various details disclosed within should not be taken to imply that
these details relate to elements that are essential components of
the various embodiments described within, even in cases where a
particular element is illustrated in each of the drawings that
accompany the present description. Further, it will be apparent
that modifications and variations are possible without departing
from the scope of the present disclosure, including, but not
limited to, embodiments defined in the appended claims. More
specifically, although some aspects of the present disclosure are
identified as particularly advantageous, it is contemplated that
the present disclosure is not necessarily limited to these
aspects.
A first aspect of the disclosure is directed to a method for
producing hierarchical mesoporous beta zeolites comprising:
providing parent beta zeolites having a molar ratio of silicon to
aluminum of from 5 to 50; mixing the parent beta zeolites with an
aqueous metal hydroxide solution; and heating the parent beta
zeolites and aqueous metal hydroxide mixture to a temperature
greater than or equal to 100.degree. C. to produce the hierarchical
mesoporous beta zeolites having an average pore size greater than 8
nanometers; where the hierarchical mesoporous beta zeolites are
produced without a templating agent or a pore-directing agent.
A second aspect of the disclosure includes the first aspect, and is
directed to the method of the first aspect, where the parent beta
zeolites have a molar ratio of silicon to aluminum.
A third aspect of the disclosure includes the first or second
aspects, and is directed to a method of the first aspect, where the
aqueous metal hydroxide is an alkali metal hydroxide or an alkali
earth metal hydroxide, or both.
A fourth aspect of the disclosure includes any of the first through
third aspects, and is directed to a method of the first aspect,
where the parent beta zeolite and aqueous metal hydroxide mixture
is heated to a temperature greater than 100.degree. C.
A fifth aspect of the disclosure includes any of the first through
fourth aspects, and is directed to a method of the first aspect,
where the parent beta zeolite and aqueous metal hydroxide mixture
is heated for a time interval of greater than or equal to 1
hour.
A sixth aspect of the disclosure includes any of the first through
fifth aspects, and is directed to a method of the first aspect,
where the produced hierarchical mesoporous beta zeolites have a
total pore volume greater than or equal to 0.30 cm.sup.3/g.
A seventh aspect of the disclosure includes any of the first
through sixth aspects, and is directed to a method of the first
aspect, where the produced hierarchical mesoporous beta zeolites
exhibit an x-ray diffraction peak at 2.THETA. from 7 degrees to 9
degrees and another x-ray diffraction peak at 2.THETA. from 21
degrees to 23 degrees.
An eighth aspect of the disclosure includes any of the first
through seventh aspects, and is directed to a method of the first
aspect, where the produced hierarchical mesoporous beta zeolites
have a peak pore size of greater than or equal to 20
nanometers.
A ninth aspect of the disclosure includes any of the first through
eighth aspects, and is directed to a method of the first aspect,
where the pH of the parent beta zeolites and aqueous metal
hydroxide mixture is greater than or equal to 12.
A tenth aspect of the disclosure includes any of the first through
ninth aspects, and is directed to a method of the first aspect,
where the concentration of the aqueous metal hydroxide solution has
a concentration from 0.01 M to 10 M.
Unless otherwise defined, all technical and scientific terms used
in this disclosure have the same meaning as commonly understood by
one of ordinary skill in the art. The terminology used in the
description is for describing particular embodiments only and is
not intended to be limiting. As used in the specification and
appended claims, the singular forms "a," "an," and "the" are
intended to include the plural forms as well, unless the context
clearly indicates otherwise.
It will be apparent to those skilled in the art that various
modifications and variations may be made to the embodiments
described within without departing from the spirit and scope of the
claimed subject matter. Thus, it is intended that the specification
cover the modifications and variations of the various embodiments
described within provided such modification and variations come
within the scope of the appended claims and their equivalents.
* * * * *